May 22, 1916 Hypoderma Deformans 285 



4 to 8 years old when uniformly infected are frequently observed 

 with the terminal portions of every principal branch in the process of 

 "brooming." The fact that the fungus sometimes occurs without the 

 least sign of a hypertrophy of the branch does not indicate that it is not 

 capable of producing such physiological and morphological changes. 

 The fact remains that on all young growth almost always the twigs 

 bearing the infected needles are abnormally swollen or branched. The 

 fungus has not been found by the writer on mistletoe brooms or on any 

 form of broom caused by insect or other animal injury. On large and 

 mature trees H. deformans very rarely occurs on any part of the tree 

 except the needles of these brooms. These abnormalities are scattered 

 promiscuously over the tree, but principally on the lower branches. 

 This indicates the nature of an infection. The more recent infections 

 on old trees are usually distributed or isolated on particular branches. 

 Serious injury seldom results from the growth of the brooms on more 

 mature growth. Very rarely may the brooms become so heavy as to 

 split-off the supporting branch. 



As the result of an examination of the witches' brooms on yellow pine 

 in the Bitter Root and Missoula River valleys, Montana, and the Coeur 

 d'Alene region of Idaho, with respect to the presence of H. defor- 

 mans on the brooms and the number, position, and distribution of the 

 brooms on the tree, the following data were obtained : 



On 107 trees examined, the average number of witches' brooms per 

 tree was 3.2. These brooms generally appeared on the lower part of the 

 crown on the side facing the prevailing winds. The average number 

 of brooms per tree bearing needles showing apothecia of H. defor- 

 mans was also 3.2. 



These figures support the view that the peculiar brooms so common on 

 yellow pine are the result of fungus infection and that the fungus respon- 

 sible is H. deformans, 



In the parts of northern Washington, Montana, and Idaho so far 

 visited, H. deformans has not been found to attack the yellow-pine 

 reproduction in as great a degree as in regions farther to the w r est 

 and south. This is probably due to a greater mixture of species. The 

 fungus is not able to spread with the same rapidity as in the more typ- 

 ical yellow-pine stands. The infected young growth usually continues 

 alive indefinitely, and deformed branches appear, eventually resulting 

 in an entire retardation of growth, and finally die. This process may 

 require several seasons, but the infected pines never attain a very large 

 size. Such deformed trees usually are attacked by bark beetles, such 

 attacks hastening their decline. 



In parts of Oregon in the yellow-pine belt the fungus was found to be 

 very destructive. During an investigation of the larch mistletoe 

 (Razoumofskya laricis Piper) in the vicinity of Sumpter, Oreg., the 



